Add central function scheduler (#609)

* Add central function scheduler

* Avoid unnecessary copies

* Lint

* Prevent more copies, store pointers

* Add never update_interval

esphome/core/scheduler.h

@@ -0,0 +1,49 @@
+#pragma once
+
+#include "esphome/core/component.h"
+#include <vector>
+
+namespace esphome {
+
+class Component;
+
+class Scheduler {
+ public:
+  void set_timeout(Component *component, const std::string &name, uint32_t timeout, std::function<void()> &&func);
+  bool cancel_timeout(Component *component, const std::string &name);
+  void set_interval(Component *component, const std::string &name, uint32_t interval, std::function<void()> &&func);
+  bool cancel_interval(Component *component, const std::string &name);
+
+  optional<uint32_t> next_schedule_in();
+
+  void call();
+
+  void process_to_add();
+
+ protected:
+  struct SchedulerItem {
+    Component *component;
+    std::string name;
+    enum Type { TIMEOUT, INTERVAL } type;
+    union {
+      uint32_t interval;
+      uint32_t timeout;
+    };
+    uint32_t last_execution;
+    std::function<void()> f;
+    bool remove;
+
+    bool operator<(const SchedulerItem &other) const;
+  };
+
+  void cleanup_();
+  bool peek_();
+  void pop_raw_();
+  void push_(SchedulerItem *item);
+  bool cancel_item_(Component *component, const std::string &name, SchedulerItem::Type type);
+
+  std::vector<SchedulerItem *> items_;
+  std::vector<SchedulerItem *> to_add_;
+};
+
+}  // namespace esphome